The present invention relates to semiconductor devices. In particular, the present invention is directed to a gallium phosphide (GaP) metal semiconductor field-effect transistor (MESFET) or a junction field-effect transistor (JFET). Gallium phosphide has the widest band gap of any of the commonly used semiconductor materials. Because of this, gallium phosphide can be used for many unique electronic devices, such as short wavelength (green) light emitting diodes and low-leakage diodes. Also, due to its low intrinsic carrier concentration, gallium phosphide devices have a potential use at very high temperatures (up to 500.degree. C.). Much of the potential of this material, however, is currently untapped due to raw material availability and processing difficulties.
Single crystal GaP has historically been expensive and in short supply. This situation is improving, but high purity material is still not readily available.
There are several processing difficulties which are encountered with GaP. First, there is no native oxide which can be used as easily as SiO.sub.2 is used in silicon semiconductor technology. A layer of SiO.sub.2 or some other similar material, therefore, must be deposited on the GaP for use in planar fabrication processing. Although there are several methods available to deposit such layers (sputtering, chemical vapor deposition, and spin-on), all of these methods are time-consuming and add complexity to the process.
Second, GaP decomposes at temperatures higher than about 600.degree. C. at one atmosphere pressure. This greatly complicates diffusions and anneals. Even though the melting point of gallium phosphide is over 1100.degree. C., special precautions must be taken when the temperature is raised above 600.degree. C. Third, diffusion impurities and techniques are very limited. Complicated doping profiles and shallow junctions are difficult to produce with diffusion techniques in GaP. Ion implantation, while it has been studied to some extent in GaP as an alternative to diffusion techniques, still requires further study.
For these reasons, the major use of GaP has been for light emitting diodes. Although some studies were performed in the 1950's and 1960's on potential use of GaP as a photodetector, it has only been in recent years that the more extensive studies of the photodetecting capabilities of GaP have been investigated.
The possible use of GaP in a field-effect type of device has been suggested on a number of occasions in the patent literature. See for example, U.S. Pat. Nos. 3,252,003; 3,304,469; 3,354,362; 3,381,187; 3,381,188; 3,753,055; and British Pat. No. 921,947. None of these references, however, describes a specific example of a GaP field-effect device or discloses the specific properties which such a device would have.